Comparison of central venous minus arterial carbon dioxide pressure to arterial minus central venous oxygen content ratio and lactate levels as predictors of mortality in critically ill patients: a systematic review and meta-analysis

OBJECTIVE: The central venousarterial carbon dioxide pressure to arterial-central venous oxygen content ratio (P(cv-a)CO(2)/C(a-cv)O(2)) is frequently used as a surrogate for tissue oxygenation. We aimed to identify and synthesize literature and quality of evidence supporting P(cv-a)CO(2)/C(a-cv)O(2) as a predictor of mortality in critically ill patients compared with lactate. METHODS: We searched several databases for studies measuring P(cv-a)CO(2)/C(a-cv)O(2) in critically ill patients. Independent investigators performed the article screening and data extraction. A random-effects metaanalysis was performed. Pooled standardized mean differences (SMD) were used to compare the prognostic ability of P(cv-a)CO(2)/C(a-cv)O(2) and lactate. RESULTS: We initially retrieved 172 studies; 17 were included for qualitative description, and 10 were included for quantitative synthesis. The mean P(cv-a)CO(2)/C(a-cv)O(2) was higher in nonsurvivors than in survivors (pooled SMD = 0.75; 95%CI 0.34 - 1.17; I(2) = 83%), as was the case with lactate levels (pooled SMD = 0.94; 95%CI 0.34 - 1.54; I(2) = 92%). Both tests were statistically significant predictors of mortality, albeit with overlapping 95%CIs between them. CONCLUSION: Moderate-quality evidence showed little or no difference in the ability of P(cv-a)CO(2)/C(a-cv)O(2), compared with lactate, to predict mortality. Nevertheless, our conclusions are limited by the considerable heterogeneity among the studies. PROSPERO registration: CRD42019130387